Technical Field of the Invention
The present invention relates to a transmission apparatus for a vehicle, to a power unit including the transmission apparatus, and to a vehicle incorporating the power unit.
Background Art
Conventionally, in regard of multiple disc clutches, there has been disclosed a structure in which three stages of clutch capacity (a fully engaged, a higher intermediate capacity, and a lower intermediate capacity) can be selected (see, for example, Patent Document 1).
Such a clutch is particularly suitable for a so-called AMT (Automated Manual Transmission) vehicle in which a shift is performed automatically. The reason lies in that, while a shift in an AMT vehicle is performed at a timing not intended by the driver, the shift shock can be reduced by selecting the clutch capacity in accordance with the throttle position, or the like, when a rotation difference is generated between the engine rotary speed (clutch outer rotary speed) and the main shaft rotary speed (clutch inner rotary speed), at the time of engagement of the clutch after movements of transmission gears.
Here, though not disclosed in detail in Patent Document 1, the clutch lift characteristic relative to the shift spindle angle on the shift-up side varies at a comparatively gentle gradient and, in addition, the three stages of the clutch capacity can be set on the basis of each clutch lift amount of a predetermined width. Therefore, even in the presence of variability regarding tolerance of the clutch or the shift spindle or the like, the shift spindle angle corresponding to a target partial clutch engagement capacity (for example, the higher intermediate capacity) can be set comparatively easily. Besides, it is also comparatively easy to adjust the shift spindle position to the target partial clutch engagement capacity.
In addition, although also not disclosed in detail in Patent Document 1, the clutch lift characteristic relative to the shift spindle angle on the shift-down side is set to rise early and increase at a steep gradient. Where there is variability regarding tolerance of the components, therefore, it is difficult to set the shift spindle angle in conformity with a target partial clutch engagement capacity (for example, the higher intermediate capacity). Besides, it is also comparatively difficult to adjust the shift spindle position to the target partial clutch engagement capacity. In the present application, the rotary angle of the shift spindle at which the clutch capacity is switched over to partial clutch engagement on the shift-down side is defined as “touch point.”
If the touch point can be learned, it can be applied to the AMT system; for example, it becomes possible to use an intermediate clutch capacity in shift control on the shift-down side as well, or to determine whether or not the clutch position has been regulated by the user or the like.
In another conventional example, a touch point learning method has been disclosed (see, for example, Patent Document 2). In Patent Document 2, there is disclosed a control for learning a touch point of a clutch by examining variations in the rotary speed of a main shaft while engaging and disengaging the clutch during when the engine is operating and the gear position is at neutral, as in the flow shown in FIG. 5 of the document.